This invention relates to thermodynamic engine system and methods for generating mechanical power for diverse utilization devices. More particularly, this invention relates to thermodynamic engine systems which utilize the temperature differential between two fluids to provide mechanical energy to follow-on machinery.
Thermodyanic engine systems and methods are known in which mechanical or other forms of energy are obtained from the thermal differential between a primary working fluid and a secondary fluid. In a typical system of this type, such as that disclosed in commonly assigned copending U.S. Pat. No. 3,986,359 for THERMODYNAMIC ENGINE SYSTEM AND METHOD filed May 29, 1973, rotary mechanical power is obtained from the temperature differential between a primary working fluid and the secondary fluid through successive energy conversion stages in each of which the thermal potential energy is converted into rotary mechanical energy. This rotary mechanical energy is then used directly to power a utilization device, such as a pump. Alternatively, the rotary mechanical energy may be converted in a known way to reciprocating mechanical energy for driving suitable follow-on devices.
Each engine stage in such a thermodynamic engine system typically comprises a heat exchanger in which the primary working fluid is heated up approximately ambient temperature by the secondary fluid and an expansion engine in which the heated primary fluid from the outlet of the associated heat exchanger is permitted to expand to produce mechanical energy.
Thermodynamic energy systems of this type are capable of operation with little or no noise pollution and, since the only exhaust product is typically an inert gas such as nitrogen, contribute no chemical pollution to the ambient atmosphere, and are thus highly desirable from an ecological standpoint.
The disclosure of the above-referenced patent application is directed to a system and method in which the primary working fluid operates on a thermodynamic cycle which comprises an initial isentropic compression, followed by successive steps of constant volume heating and isentropic expansion. As noted in the application, the total amount of useful work obtainable with this thermodynamic cycle is substantially greater than that obtainable with prior thermodynamic engines utilizing constant pressure heating cycles, and thus the system and method of the application provides superior performance to known engines using a relatively low temperature fluid as the primary working fluid.
Ideally, even more efficient thermodynamic engines than those employing the thermodynamic cycle of the application supra are theoretically possible. Specifically, for engines using a low temperature fluid as the primary working fluid, the maximum work theoretically obtainable is realized if the working fluid is heated to the temperature of the heat source (typically the secondary fluid or ambient temperature) and then expanded isothermally rather than isentropically or adiabatically. As a practical matter it is not possible, to heat the primary working fluid to exactly ambient temperature and maintain the primary fluid at a temperature which differs from ambient temperature by a nominal amount, typically a few degrees centigrade. Efforts to date, however, to provide operable thermodynamic engines using an isothermal or quasi-isothermal thermodynamic cycle for a low temperature primary working fluid have not met with success.